Polypengeneration und Entwicklungsgeschichte vonEucheilota maculata (Thecata-Leptomedusae)

Polyps and medusae differ in regard to habitats, evolution, and morphological structures. In order to replace the former taxonomic systems which deal with polyp and medusa generations separately, by a single valid classification including both generations, knowledge of all essential life history phases is necessary. Modern methods of culturing marine hydroids are outlined briefly. Successful culturing provides the means to link formerly unidentified polyps or medusae with one another. The present paper is concerned with the hydroidEucheilota maculata Hartlaub, the medusa of which is common in the southern North Sea. The polyps formerly unknown have been reared from fertilized eggs of the medusae. They were raised to full size, formed colonies, and produced gonangia and medusae. Thus the morphology of the single polyp, the polyp colony, and of the young medusa could be investigated in detail. The nematocyst equipment of the two generations and of all developmental stages is described as well as the number of chromosomes. The systematic position of the genusEucheilota is discussed and the diagnosis of the speciesE. maculata, including the two generations, given.     

Bau und Lebensgeschichte des Polypen vonTripedalia cystophora (Cubozoa,class. nov., Carybdeidae) und seine Bedeutung für die Evolution der Cnidaria

FollowingHaeckel (1880), most zoologists have grouped the Cubomedusae with the class Scyphozoa. However, the actual systematic position and evolution of the Cubomedusae remained unclear because essential phenomena of the life cycle, i. e. life history and structure of the polyp generation and the process of medusa formation were unknown. Successful cultivation of the Carribean larviparousTripedalia cystophora Conant, 1898 elucidated for the first time the complete life cycle of a cubomedusa. Primary polyps could be raised from planulae which were transferred by air mail from La Parguera, Puerto Rico. The sessile polyp is solitary. Its morphology, anatomy, and behaviour are described. The body (length 0.6–1.0 mm) is radially constructed without any trace of tetramerous structures. 6 to 11 solid capitate tentacles insert in one circle, above which the body ends in a long contractile snout-like mouth cone (proboscis). The body is sac-like without gastric septa or gastric pockets; its base is enveloped by a small cup of thin, structureless periderm. Asexual reproduction by which the stock is enlarged quickly envolves lateral budding of small secondary polyps. After detachment these small polyps go through a creeping phase. The fully grown polyp shows a remarkable behavioural plasticity as it can migrate and change into an inactive encysted stage. The whole polyp metamorphoses into a single medusa. All externally visible metamorphosis phases are described. First, the polyp's body becomes tetramerous due to 4 longitudinal folds. The tentacles congregate into 4 groups, each in one quadrant. While the distal parts of the tentacles are resorbed, their bases develop into 4 perradial sensory organs (rhopalia). Interradially, 4 new tentacles are formed and become the primary tentacles of the medusa. Simultaneously, the complete body of the polyp transforms into the bell of the medusa. At the end of the metamorphosis which takes 5 to 6 days at 25 to 27° C, the young medusa begins to pulsate quickly and swims away leaving behind the empty peridermal cup. The morphology of the young medusa is described.T. cystophora has a tricnidom of basitrich haplonemes, holotrich haplonemes, and heterotrich microbasic euryteles. The ecology of both, polyp and medusa generation, is briefly outlined. A critical comparison between the polyp and medusa ofT. cystophora and the Scyphozoa and Hydrozoa reveals important differences. Consequently, a new class, Cubozoa, must be established and given the evolutionary position between Scyphozoa and Hydrozoa. Diagnoses are presented for the polyp ofT. cystophora and the class Cubozoa.     

Telomerase activity is not related to life history stage in the jellyfish Cassiopea sp.

The polyp (scyphistoma) of the jellyfish Cassiopea sp. can be maintained in culture for a long time, as polyps repeatedly reproduce asexually via formation of vegetative buds or propagules. The medusa, which is the sexually reproducing stage, typically has a relatively short life span. As a first step to understand the difference in life spans of the polyp and medusa stages of Cassiopea sp., we measured telomerase activity in different life cycle stages. We found telomerase activity in tissues of aposymbiotic polyps and propagules and symbiotic ephyrae (newly budded medusae) and adult medusae. No significant difference in telomerase activity was found between polyps and the bell region of the medusae. The cloned elongation products of the stretch PCR contained the TTAGGG repeats suggesting that the jellyfish has the ‘vertebrate’ telomere motif (TTAGGG)_n. This is the first study to show that somatic tissues of both polyp and medusa stages of a cnidarian had telomerase activity. Telomerase activity in somatic tissues may be related to the presence of multipotent interstitial cells and high regenerative capacity of cnidarians.     

Taxonomic characters from the polyp tubes of coronate medusae (Scyphozoa,Coronatae)

The tubes of the polyp stages of all known species of the family Nausithoidae have been examined to find characters useful for specific identification. Such characters comprise both internal and external structures of the chitinous exoskeleton, measurements of the periderm, and the shape of the tubes defined by the Formquotient. A key for the polyp generation is given based on these characters. The long-term rearing of several species and elucidation of their life cycles has also enabled a key to the medusa generation of the Nausithoidae to be constructed. Stephanoscyphistoma gen. nov. is proposed for the polyps of all species of coronates of uncertain medusa genus.     

Morphological and ultrastructural analysis of Turritopsis nutricula during life cycle reversal

The hydrozoa life cycle is characterized, in normal conditions, by the alternation of a post-larval benthic polyp and an adult pelagic medusa; however, some species of Hydrozoa react to environmental stress by reverting their life cycle: i.e. an adult medusa goes back to the juvenile stage of polyp. This very uncommon life cycle could be considered as some sort of inverted metamorphosis. A morphological study of different stages during the reverted life cycle of Turritopsis nutricula led to the characterization of four different stages: healthy medusa, unhealthy medusa, four-leaf clover and cyst. The ultrastructural study of the cellular modifications (during the life cycle reversion of T. nutricula) showed the presence of both degenerative and apoptotic processes. Degeneration was prevalent during the unhealthy medusa and four-leaf clover stages, while the apoptotic rate was higher during the healthy medusa and cyst stages. The significant presence of degenerative and apoptotic processes could be related to the occurrence of a sort of metamorphosis when an adult medusa transforms itself into a polyp.     

Larval necrophilia: the odd life cycle of a pandeid hydrozoan in the Weddell Sea shelf

Colonies of an athecate hydroid were found at six stations in the high Antarctic (Weddell Sea) growing on dead specimens of Flabelligera mundata (Annelida, Polychaeta). All living specimens of F. mundata at the same stations were free of epibionts. Transplantation experiments showed that hydropolyps did not produce stolons on substrates other than the epidermal jelly coat and chetae of dead F. mundata specimens. The largest colonies (>1,000 polyps) producing medusa buds were cultured until medusa liberation: growth of medusae was then surveyed for the next 5 weeks, but development of adult features was extremely slow. Young medusae were ascribed to the suborder Pandeida by the presence of two main characters, namely (1) hollow marginal tentacles, and (2) a mouth with four simple lips. Considering polyp and young medusa features, this species is acknowledged as newly recorded for the Southern Ocean, and assigned to the genus Neoturris (Hydroidomedusae, Pandeidae).     

On the distribution of ‘gonionemus vertens’ a. Agassiz (Hydrozoa,Limnomedusae), a new species in the eelgrass beds of Lake Grevelingen (S.W. Netherlands)

Summary Data about morphology, life history and habits ofGonionemus vertens A. Agassiz (Hydrozoa, Limnomedusae) are given. The distribution of the species is treated in more detail, especially its mechanism in relation to large-scale (global) and small-scale (local) range extensions.The species is endemic in the coastal North Pacific Ocean, possessing a strictly littoral medusa stage (bound to eelgrass beds and algal belts) and a very small sessile solitary polyp phase (attached to stones and shells).The hypotheses trying to explain the spread to Western Europe and the Atlantic coast of North America strongly suggest human influences,i.e. distribution of the polyp via oyster transports (EDWARDS, 1976) and transport of the polyp as a member of the fouling community on ships hulls (TAMBS-LYCHE, 1964). Arguments pro and contra these hypotheses are evaluated. The occurrence ofGonionemus polyps in offshore waters, as mentioned by EDWARDS (1976) but not further discussed by this author, deserves more attention.It is the assumed occurrence of the polyps in shallow as well as in deeper waters with strong tidal movements that explains satisfactorily the previous and recent findings of the medusa in the S.W.-Netherlands. The medusa has been found in theZostera marina beds of the saline Lake Grevelingen. From 1976 onwards the abundance of the medusa increased synchronously with the extension of the eelgrass beds. Medusae were collected during the summer of 1980, fed with isopod crustaceans or mussel meat and kept alive for several months in seawater aquaria in the lab. Polyps have not yet been observed.Communication no. 211 of the Delta Institute for Hydrobiological Research.     

Molecular characterization of aspartylglucosaminidase,a lysosomal hydrolase upregulated during strobilation in the moon jellyfish,Aurelia aurita

The life cycle of the moon jellyfish, Aurelia aurita, alternates between a benthic asexual polyp stage and a planktonic sexual medusa (jellyfish) stage. Transition from polyp to medusa is called strobilation. To investigate the molecular mechanisms of strobilation, we screened for genes that are upregulated during strobilation using the differential display method and we identified aspartylglucosaminidase (AGA), which encodes a lysosomal hydrolase. Similar to AGAs from other species, Aurelia AGA possessed an N-terminal signal peptide and potential N-glycosylation sites. The genomic region of Aurelia AGA was approximately 9.8 kb in length and contained 12 exons and 11 introns. Quantitative RT-PCR analysis revealed that AGA expression increased during strobilation, and was then decreased in medusae. To inhibit AGA function, we administered the lysosomal acidification inhibitors, chloroquine or bafilomycin A1, to animals during strobilation. Both inhibitors disturbed medusa morphogenesis at the oral end, suggesting involvement of lysosomal hydrolases in strobilation.     

An endogenous green fluorescent protein–photoprotein pair in Clytia hemisphaerica eggs shows co-targeting to mitochondria and efficient bioluminescence energy transfer

Green fluorescent proteins (GFPs) and calcium-activated photoproteins of the aequorin/clytin family, now widely used as research tools, were originally isolated from the hydrozoan jellyfish Aequora victoria. It is known that bioluminescence resonance energy transfer (BRET) is possible between these proteins to generate flashes of green light, but the native function and significance of this phenomenon is unclear. Using the hydrozoan Clytia hemisphaerica, we characterized differential expression of three clytin and four GFP genes in distinct tissues at larva, medusa and polyp stages, corresponding to the major in vivo sites of bioluminescence (medusa tentacles and eggs) and fluorescence (these sites plus medusa manubrium, gonad and larval ectoderms). Potential physiological functions at these sites include UV protection of stem cells for fluorescence alone, and prey attraction and camouflaging counter-illumination for bioluminescence. Remarkably, the clytin2 and GFP2 proteins, co-expressed in eggs, show particularly efficient BRET and co-localize to mitochondria, owing to parallel acquisition by the two genes of mitochondrial targeting sequences during hydrozoan evolution. Overall, our results indicate that endogenous GFPs and photoproteins can play diverse roles even within one species and provide a striking and novel example of protein coevolution, which could have facilitated efficient or brighter BRET flashes through mitochondrial compartmentalization.     

Cytologische Veränderungen während der Metamorphose des CubopolypenTripedalia cystophora (Cubozoa,Carybdeidae) in die Meduse

The life cycle ofTripedalia cystophora includes a sessile saclike polyp — the asexual reproducing form — and a pelagic tetraradial medusa — the sexually reproducing generation. Medusan development can be induced by temperature increase. It reveals neither budding nor strobilation, but a real metamorphosis of a polyp to only one medusa. According to morphological and anatomical criteria the metamorphosis can be subdivided into four different stages: (1) four longitudinal furrows segment the polyp, the tentacles of which are apportionated on the four quadrants of the body. (2) The subumbrellar cavity develops by invagination of the peristom; the relicts of the fused tentacles change to four rhopalia buds. (3) Medusan architecture including four new interradial tentacles, four rhopalia and the subumbrellar swimming musculature is completed. (4) A young tetraradial medusa starts swimming. Ultrastructural analysis of those metamorphic stages show the different processes of morphogenesis: (a) Gastrodermal cells — absorptive and spumous cells — undergo transdifferentiation and proliferation to medusan cells of the same structure and function. (b) Epidermal cells, excluding the epithel muscle cells, dissociate and are autolytically withdrawn. Dedifferentiated epithel muscle cells — interstitial cells — regain the ability to develop a complete new set of somatic cells, not originally present in the polyp. They include amongst others cross-striated muscle cells, medusan typic nematocyts and particularly sensory and nervous cells. Those cells establish a nervous system with lens-eyes, simple ocelli, statocysts, diffuse nerve net and an additional nerve ring.     

First Description of Sulphur-Oxidizing Bacterial Symbiosis in a Cnidarian (Medusozoa) Living in Sulphidic Shallow-Water Environments

BackgroundSince the discovery of thioautotrophic bacterial symbiosis in the giant tubeworm Riftia pachyptila, there has been great impetus to investigate such partnerships in other invertebrates. In this study, we present the occurrence of a sulphur-oxidizing symbiosis in a metazoan belonging to the phylum Cnidaria in which this event has never been described previously.Conclusions/SignificanceThis is the first report describing the occurrence of a sulphur-oxidizing symbiosis in a cnidarian. Furthermore, of the two adult morphologies, the polyp and medusa, this mutualistic association was found restricted to the polyp form of Cladonema sp.     

Life Cycle Reversal in Aurelia sp.1 (Cnidaria,Scyphozoa)

The genus Aurelia is one of the major contributors to jellyfish blooms in coastal waters, possibly due in part to hydroclimatic and anthropogenic causes, as well as their highly adaptive reproductive traits. Despite the wide plasticity of cnidarian life cycles, especially those recognized in certain Hydroza species, the known modifications of Aurelia life history were mostly restricted to its polyp stage. In this study, we document the formation of polyps directly from the ectoderm of degenerating juvenile medusae, cell masses from medusa tissue fragments, and subumbrella of living medusae. This is the first evidence for back-transformation of sexually mature medusae into polyps in Aurelia sp.1. The resulting reconstruction of the schematic life cycle of Aurelia reveals the underestimated potential of life cycle reversal in scyphozoan medusae, with possible implications for biological and ecological studies.     

Fish assemblage structure in urban streams of Puerto Rico: the importance of reach- and catchment-scale abiotic factors

Cotylorhiza tuberculata is a common symbiotic scyphozoan in the Mediterranean Sea. The medusae occur in extremely high abundances in enclosed coastal areas in the Mediterranean Sea. Previous laboratory experiments identified thermal control on its early life stages as the driver of medusa blooms. In the present study, new ecological aspects were tested in laboratory experiments that support the pelagic population success of this zooxanthellate jellyfish. We hypothesized that planulae larvae would have no settlement preference among substrates and that temperature would affect ephyra development, ingestion rates and daily ration. The polyp budding rate and the onset of symbiosis with zooxanthellae also were investigated. Transmission electron microscopy revealed that zooxanthella infection occurred by the polyp stage. Our results showing no substrate selectivity by planulae and high polyp budding rates in high temperatures suggest increased benthic polyp populations, which would lead to higher medusa abundances. Rates of transition from ephyrae to medusae and the feeding of early medusa stages also increased with temperature. Continuing changes in coastal ecosystems such as future climate warming and marine construction may lead to increased populations of jellyfish to the detriment of fish globally.     

Stephanoscyphus planulophorus n. spec., ein neuer Scyphopolyp mit einem neuen Entwicklungsmodus

A new solitary species ofStephanoscyphus (order Coronatae) is described. It has been collected in submarine caves of the rocky shore near Marseille, Mediterranean Sea, where it lives attached to colonies of corals at a depth of 10 to 20 m. The essential characteristics of the peridermal tube and the soft body are outlined. They are not sufficient to distinguish significantly the new species from others of the same genus. Identification was possible by the observation of a unique way of development which is characterized by the complete reduction of the free swimming medusa generation. First, the strobilation phase undergoes normal development whereby a chain of numerous ephyra-like stages is originated in the tube of the polyp. Simultaneously, its head is transformed into an opercular apparatus in the normal way whereby the aperture of the tube is closed completely. The strobilation stages must be considered as true young ephyrae because of their flat shape, the regularly formed marginal lappets and contraction movements. Contrary to the normal development, the ephyrae metamorphozise directly to ciliated free swimming planulae. After a long period of incubation, the planulae hatch from the tube and begin a planctonic way of life for a period of about 14 to 50 days. They attach then to the substratum in the normal way and develop into young polyps with a basic disk and small peridermal tube. Thus, the life cycle is completed. Because of the existence of a strobilation phase and the production of ephyrae the mode of development must be considered as a reduced metagenesis. The problem of the existence and special realization of the sexual phase remains unsolved. The diagnosis of the new species is given, and the systematical, evolutionary and ecological aspects of the new mode of development are discussed.     

Nematocysts and Taxonomy in Laomedea, Gonothyraea and Obelia (Hydrozoa, Campanulariidae)

The cnidoms of Laomedea flexuosa, Gonothyraea loveni, Obelia geniculata, O. longissima and O. dichotoma were studied by light and scanning electron microscopy to find out whether the nematocysts could be used as taxonomic characters. Three b-rhabdoid heteroneme nematocysts (microbasic b-mastigophore) and three isorhizous haploneme nematocysts (atrichous isorhiza) were distinguished. A small b-rhabdoid nematocyst with spindle-shaped capsule occurred in all the species examined. In the polyp and planula of G. loveni , and the planula of L. flexuosa it was the only nematocyst present. Specific for L. flexuosa was a b-rhabdoid with curved capsule. In the polyp and newly-liberated medusa of O. longissima another b-rhabdoid appeared with bean-shaped capsule and markedly long spines at the distal tube. The polyp and newly-liberated medusa of O. dichotoma were characterized by two different isorhizas. A special type of isorhiza occurred in the polyp of O. geniculata . The curved capsules of the different isorhizas varied somewhat in shape and size. Differences in nematocyst structure and occurrence are presumed to provide characters for taxonomy. Thus, O. dichotoma and O. Iongissima are regarded as separate species due to their distinctly different nematocysts, in conjunction with other morphological and ecological differences.     

Synchronized release of medusae from three species of hydrozoan fire corals

 The release of medusae from three hydrozoan fire corals, Millepora dichotoma, M. murrayi and M. platyphylla, was investigated at three sites in southern Taiwan from February 1994 to July 1995. All three species were gonochoristic, and developed and released several batches of medusae between April and May. The duration of open ampulla appearing on the surface of coralla was short, about three months, and could be used to infer the reproductive season of the fire corals between April and May. No obvious lunar cycles of medusa release were found in these species. Medusa release started before dark at approximately 17:00 h and continued for several hours. Males began releasing medusae earlier than females. Synchronization of medusa release between colonies, i.e., the probability of occurring on the same nights, was significantly higher within a species than between different species. Hybridization in nature among the three species is, therefore, unlikely due to segregation in the spawning dates. Moreover, the synchronization within each species was often significantly higher within versus between sites. The free-swimming medusae released gametes within approximately one hour, and the spent medusae lived for a few more hours. Medusae may facilitate fertilization rates as a result of an apparently negatively geotactic swimming response that results in medusa aggregation at the surface. No differences in the sizes of medusae, eggs and sperm were detected among the three species; however, some characteristic differences of medusa nematocysts were found. Accepted: 25 September 1997